Thank you Lee and Ray for your comments and advices. Will keep experimenting to see what works best. A pier sounds like a very good idea - but will need to wait with that until I have my own backyard
I am using a reducer so image scale is 1.33"/px. I have found that occasional adjustement of aggression and min movement throughout imaging session (same target) are needed with my equipment to get the best possible guiding. Also, additional calibration after a few hours can help too.